1. Field of the Invention
The present invention relates generally to disc cartridges and more particularly to a disc cartridge in which a magneto-optical disc is rotatably accommodated in a hermetic-fashion for recording and/or reproduction.
2. Description of the Prior Art
An optical disc recording and/or reproducing apparatus has been known, in which an optical disc, formed of a disc substrate and an optical record medium formed thereon, is used as a high density information recording disc and information is recorded on and/or reproduced from the optical disc by the impingement of a laser light on this optical disc. The family of the optical disc might be a read-only type optical disc (for example, a compact disc, etc.) from which an information can be reproduced only, a write-once type optical disc in which information can be written, and a rewritable-type optical disc (for example, a magneto-optical disc) in which information can be rewritten.
According to these optical discs, the recording and/or reproduction is generally carried out under the condition that the optical disc is loaded onto a recording and/or reproducing apparatus. When the optical disc is treated in this way, there is then a possibility that the optical disc surface will be smudged by fingermarks or that the optical disc surface will be damaged by scratches and so on. This causes an error in the recording or reproduction. To solve the above-noted problem, it is proposed to use a disc cartridge which rotatably accommodates an optical disc. This disc cartridge is disclosed, for example, in Japanese Laid-open Utility Model Gazette No. 61-174078.
This type of disc cartridge is designed so that it can be used sufficiently under normal circumstances. However, this type of disc cartridge can not demonstrate its efficiency sufficiently under some special circumstance such as in the cabin of an aircraft where atmospheric pressure is changed considerably. To eliminate the above-noted defect of the prior-art disc cartridge, a hermetic-type disc cartridge is proposed, in which the optical disc is accommodated in an airtight fashion so that it can be used in the special circumstance (see Japanese Published Patent Gazette No. 60-48818 and U.S. Pat. No. 4,535,434, etc.).
The magneto-optical disc in which an information signal can be rewritten needs external auxiliary magnetic field to record an information signal. Accordingly, in any of the disc cartridge&in which the magneto-optical disc is accommodated and the hermetic-type disc cartridge, external magnetic field generating means is opposed to the magneto-optical disc from the outside of the housing and a magnetic field from the external magnetic field generating means is supplied to the record medium surface of the magneto-optical disc through the housing.
In the prior-art disc cartridge, however, the inside spacing of the housing causes the external magnetic field generating means provided outside of the housing and the magneto-optical disc provided inside of the housing to become distant from each other by a predetermined distance, whereby the magnetic field from the external magnetic field generating means can not be supplied with sufficient flux strength to the record medium surface of the magneto-optical disc. The magneto-optical recording can not be therefore carried out positively.
In particular, the hermetic-type disc cartridge is frequently used under some special circumstance such as the cabin of an aircraft in which atmospheric pressure is considerably changed. In that event, the prior-art disc cartridge has a space in its inside so that, when the disc cartridge is applied with internal or external pressure, the housing of the disc cartridge is caused to be warped, thereby deforming the disc cartridge considerably. As a result, upon use, the disc cartridge thus deformed can not be loaded onto a disc drive apparatus. Further, it is frequently observed that, when the disc cartridge is considerably deformed, trouble occurs when trying to rotate the disc accommodated within the disc cartridge.